Antimicrobial resistance and genetic characterization of Clostridium perfringens isolated from companion animals in South Korea, 2018-2024.

Clostridium perfringens is an emerging pathogenic bacterium associated with various gastrointestinal diseases in humans and animals. We aimed to investigate the prevalence, antimicrobial resistance, and molecular characteristics of C. perfringens isolated from companion animals. A total of 743C. perfringens isolates were recovered from diarrheal feces of dogs (n = 516) and cats (n = 227) in South Korea between 2018 and 2024. The majority of isolates were resistant to tetracycline (58.1%) and clindamycin (11.3%). Nonetheless, ampicillin, cefotetan, cefoxitin, chloramphenicol, metronidazole, penicillin, and piperacillin resistance were low (0.1-6.2%). Toxinotyping showed that 97.4% of C. perfringens belong to type A, comprising the toxin gene cpa, and 1.7% to type F, encompassing cpa and cpe. Multi-locus sequence typing of 116C. perfringens isolates resistant to metronidazole, penicillin, or clindamycin revealed that ST102 (11.1%) was the most consistently prevalent among 82 STs, clustering in seven clonal complexes. Notably, we identified the optrA-encoding plasmid in companion animals for the first time. The plasmids harbor various antimicrobial resistance genes, including those for phenicols, macrolides, tetracyclines, and lincomycins. Transposable elements IS1216E and ISEfa5 were detected in the plasmids, facilitating the dissemination of resistance. Taken together, C. perfringens carrying resistance and toxin genes could pose human health hazards.